Pyrochlore-type catalysts for the reforming of hydrocarbon fuels

ABSTRACT

A method of catalytically reforming a reactant gas mixture using a pyrochlore catalyst material comprised of one or more pyrochlores having the composition A 2-w-x A′ w A″ x B 2-y-z B′ y B″ z O 7-Δ . Distribution of catalytically active metals throughout the structure at the B site creates an active and well dispersed metal locked into place in the crystal structure. This greatly reduces the metal sintering that typically occurs on supported catalysts used in reforming reactions, and reduces deactivation by sulfur and carbon. Further, oxygen mobility may also be enhanced by elemental exchange of promoters at sites in the pyrochlore. The pyrochlore catalyst material may be utilized in catalytic reforming reactions for the conversion of hydrocarbon fuels into synthesis gas (H 2 +CO) for fuel cells, among other uses.

RELATION TO OTHER APPLICATIONS

This patent application claims priority to U.S. Provisional PatentApplication No. 61/044,537 filed Apr. 14, 2008, submitted by Berry, etal., which is hereby incorporated by reference in its entirety.

STATEMENT OF GOVERNMENTAL SUPPORT

The United States Government has rights in this invention pursuant tothe employer-employee relationship of the Government to the inventors asU.S. Department of Energy employees and site-support contractors at theNational Energy Technology Laboratory.

TECHNICAL FIELD

A method of catalytically reforming a reactant gas mixture using apyrochlore catalyst material comprised of one or more pyrochlores havingthe composition A_(2-w-x)A′_(w)A″_(x)B_(2-y-z)B′_(y)B″_(z)O_(7-Δ).Distribution of catalytically active metals throughout the structure atthe B site creates an active and well dispersed metal locked into placein the crystal structure. This greatly reduces the metal sintering thattypically occurs on supported catalysts used in reforming reactions, andreduces deactivation by sulfur and carbon. Further, oxygen mobility mayalso be enhanced by elemental exchange of promoters at sites in thepyrochlore. The pyrochlore catalyst material may be utilized incatalytic reforming reactions for the conversion of hydrocarbon fuelsinto synthesis gas (H₂+CO) for fuel cells, among other uses.

BACKGROUND OF THE INVENTION

The combustion of fossil fuels (i.e. coal, petroleum and natural gas) isthe primary source of power production in transportation and stationarypower applications. However, combustion is relatively inefficientcompared to advanced processes, due to significant heat and frictionallosses during the conversion process. Furthermore, the products ofcombustion, including NO_(x), SO_(x), particulate matter, CO, and CO₂,are the subject of current and anticipated regulations. There istherefore an interest in energy conversion technologies that utilizefossil fuel resources more efficiently with less of an environmentalimpact.

For example, one effective means of using fossil fuels as an energysource is to catalytically reform them into synthesis gas (H₂+CO), whichcan then be converted to electrical power in a solid oxide fuel cell(SOFC). Of the available alternative technologies, no other energyproduction method offers the combination of clean energy and efficiencyprovided by a SOFC. Because a wide range of fuels can be used, SOFCshave proven to be versatile, and can be used in such applications asauxiliary power units (APUs) for diesel trucks, as well as decentralizedstationary power for commercial and military applications

Three main catalytic reforming reactions can be used to converthydrocarbon fuels into synthesis gas (H₂+CO) for fuel cells: steamreforming (SR), catalytic partial oxidation (CPOX), and autothermalreforming (ATR).

SR C_(n)H_(m) + H₂O → H₂ + CO ΔH > 0 CPOX C_(n)H_(m) + O₂ → H₂ + CO ΔH <0 ATR C_(n)H_(m) + H₂O + O₂ → H₂ + CO ΔH~0

The choice of reforming reaction depends on the application. For fuelcell applications listed where fast light-off, kinetics, quick dynamicresponse and compactness are of most benefit, CPOX is generally favored.For applications that favor efficiency, SR is generally favored due toits ability to utilize system heat in the reformer. In otherapplications, ATR or some other degree of oxidative steam reforming(OSR) is desired because of the ability to control the reformate gascomposition and minimize heat transfer limitations.

A wide variety of hydrocarbons can be reformed to produce synthesis gas,including natural gas, coal, gasoline and diesel. Of these fuels, dieselis an attractive and practical choice in many cases, because of its highhydrogen density and well developed distribution infrastructure. Again,the choice is application dependent. However, it is also the mostdifficult fuel to reform because diesel fuel is a mixture of a widevariety of paraffin, naphthene, aromatic and organosulfur compounds,each of which reacts differently in a CPOX reaction sequence. Thespecific nature of each of these components, i.e. chain length ofn-paraffins, substituents attached to hydrocarbon rings, and degree ofsaturation of aromatic compounds affects the overall fuel conversion.Some of these constituents are also known to deactivate reformingcatalysts through carbon formation and sulfur poisoning.

Thus, the challenge in reforming diesel is to develop a catalyst thatcan maintain high product selectivity to H₂ and CO in the presence ofaromatics and sulfur species, while being robust enough to operate atreforming conditions, typically 800-1000° C.

Reforming catalysts have typically been nickel or Group-VIII noblemetals supported by various high surface area oxide substrates such asaluminas, silicas, and mixed metal oxides. In some cases, pyrochloresare included as suitable supports for the catalytically active metals.See e.g. U.S. Pat. No. 6,238,816, issued to Cable et al, issued May 29,2001; U.S. Pat. No. 6,409,940, issued to Gaffney et al, issued Jun. 25,2002. The metal is dispersed onto the support surface in smallcrystallites to maximize the amount of active metal exposed. However,this design of the catalyst may be predisposed to carbon formation anddeactivation by sulfur. The adsorption of sulfur and carbon has beenshown to be structure sensitive. Specifically, both carbon and sulfuradsorption have been linked to the metal cluster size, with largerclusters more prone to deactivation. See Barbier et al, “Effect ofpresulfurization on the formation of coke on supported metal catalysts,”Journal of Catalysis, 102 (1986), among others.

Oxide-based catalysts such as perovskites (ABO₃) have been examined asalternatives to noble metal catalysts for at least the autothermalreforming of a JP-8 fuel surrogate and dry (CO₂) reforming of methane bysubstituting various metals into the A and B sites. See Liu andKrumpelt, “Activity and Structure of Perovskites as Diesel-ReformingCatalysts for Solid Oxide Fuel Cell,” Int. J. Appl. Ceram. Technol., Vol4 (2), (2005), and see Erri et al, “Novel Perovskite-based catalysts forautothermal JP-8 fuel reforming,” Chemical Engineering Science, 61(2006), among others. Although the perovskite catalysts did exhibitgenerally favorable activity and coking resistance in the dry reformingcase, analyses following catalytic tests showed that the perovskitestructure is not maintained and separation of the active metals from thestructure is observed. Findings indicate that the structural changesobserved in the catalyst occurred primarily during the initial reductionstage. No indication was given regarding long-term stability of thatcatalyst system.

In another class of oxide-based catalysts, it has been observed thatbulk ruthenate pyrochlores (Ln₂Ru₂O₇: Ln is a lanthanide) are highlyactive for both dry reforming and CPOX of methane. See, Ashcroft et al.,“An in situ, energy-dispersive x-ray diffraction study of natural gasconversion by carbon dioxide reforming,” Journal of Physical Chemistry97 (1993), among others. However, despite high activity, post-runcharacterization of this particular catalyst revealed that the bulkPr₂Ru₂O₇ pyrochlore was not stable under CPOX conditions. Catalyticactivity of the material was likely derived from the decomposition ofthe pyrochlore phase under the reducing reaction conditions, whichcreated a Ru-metal enriched surface and a defect fluorite structure inthe bulk due to the increased Pr—Ru ratio in the bulk. Decomposition wasalso observed on the ruthenate catalysts used for the dry reforming ofmethane. The structural instability of this particular material is notdesirable for reforming reactions like CPOX, and likely occurred as aresult of selecting a metal (Ru) to occupy entire B-site that is highlyreducible. During the break down of the pyrochlore or oxide-basedcatalyst structure, Ru or active metal migration to the surface leads tothe formation of an essentially supported metal catalyst, which shouldbe avoided due to the increased tendency towards deactivation by carbonand sulfur. There is also a tendency toward further metal migration orvaporization, leading to long-term permanent catalytic activity loss.

Similarly, other A₂B₂O₇ pyrochlores have been disclosed for use ascatalysts in the reforming of hydrocarbons. These catalysts are limitedto A₂B₂O₇ structures and emphasize the catalytic nature of binary mixedmetal oxides. Use of additional dopants at the A and B sites in order toenhance the catalytic nature of the crystal structure are not disclosed.Further, in some cases, the catalytic activity of these binary mixedoxides stems largely from B-site migration and the metal-enrichedsurface which results. See e.g., U.S. Pat. No. 5,500,149, issued toGreen et al, issued on Mar. 19, 1996; U.S. Pat. No. 5,149,464, issued toGreen et al, issued on Sep. 22, 1992; U.S. Pat. No. 5,015,461, issued toJacobson et al, issued on May 14, 1991; U.S. Pat. No. 4,959,494, issuedto Felthouse, issued on Sep. 25, 1990.

However, many pyrochlores display chemical and thermal stability withhigh melting points and show the mechanical strength necessary toaccommodate metal substitutions necessary for high catalytic activity.The development of a pyrochlore catalyst with spatially distributedactive metal components in a structure that resists decomposition athigh reforming temperatures would provide a more durable and effectivecatalyst compared to simple supported metal clusters. Resistance todecomposition would maintain the spatially distributed active metalcomponents as structural components in the pyrochlore, and significantlyminimize the migration of active metal components to the surface. Thiscould largely avoid the undesirable defacto formation of a supportedmetal catalyst from some initially oxide-based catalyst systems at thereforming conditions, and could greatly reduce the tendency towardsdeactivation by carbon and sulfur. It would also hold potential as along-life reforming catalyst.

Accordingly, it is an object of this disclosure to provide a method ofcatalytically reforming a reactant gas mixture using a pyrochlorecatalyst material stable under reaction conditions.

It is a further object of this disclosure to catalytically reform areactant gas mixture using a pyrochlore catalyst material whichmaintains high product selectivity to H₂ and CO in the presence ofaromatics and sulfur species.

It is a further object of this disclosure to catalytically reform areactant gas mixture using a pyrochlore catalyst material that resistsboth sulfur poisoning and carbon deposition.

It is a further object of this disclosure to catalytically reform areactant gas mixture using a pyrochlore catalyst material that minimizescatalytically active metal migration to the surface, leading to theformation of a supported metal catalyst.

It is a further object of this disclosure to catalytically reform areactant gas mixture using a pyrochlore catalyst material wheresubstitution of elements in A sites and/or B sites creates defects inthe crystal structure and improves the lattice oxygen mobility.

These and other objects, aspects, and advantages of the presentdisclosure will become better understood with reference to theaccompanying description and claims.

SUMMARY OF INVENTION

Provided herein is a method for catalytically reforming a reactant gasmixture using a pyrochlore catalyst material comprised of one or morepyrochlores having the compositionA_(2-w-x)A′_(w)A″_(x)B_(2-y-z)B′_(y)B″_(z)O_(7-Δ). wherein:

-   -   A is a trivalent ion of an element selected from the group        consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Er, Tm,        Yb, Lu, Bi, Sc, Y, In, and Tl,    -   A′ is a trivalent ion of an element not equivalent to A and        selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm,        Eu, Gd, Tb, Dy, Er, Tm, Yb, Lu, Bi, Sc, Y, In, and Tl, and        wherein 0≦w≦1,    -   A″ is a divalent ion selected from the group consisting of Mg,        Ca, Sr, and Ba, and wherein 0≦x<1 and w+x≦1,    -   B is a tetravalent ion of an element selected from the group        consisting of Ti, Cr, Mn, Zr, Mo, Tc, Rh, Pd, Hf, Os, Ir, Pt,        Si, Ge, Sn, and Pb,    -   B′ is a trivalent ion or a tetravalent ion of an element        selected from the group consisting of Mo, Fe, Os, Ru, Co, Rh,        Ir, Ni, Pd, Pt, Cu, Re and V, wherein if B′ is a tetravalent ion        then B′ is an element not equivalent to B, and wherein 0<y≦1,    -   B″ is a divalent ion, a trivalent ion, or a tetravalent ion of        an element selected from the group consisting of Mg, Ca, Sr, Ba,        Y, Ce, Re, Cr, Ti, Zr, Hf, Ni, Co, V, and Mo, wherein if B″ is a        trivalent ion B″ is an element not equivalent to B′, and if B″        is a tetravalent ion than B″ is an element not equivalent to B′        and not equivalent to B, wherein 0≦z<1 and y+z≦1, and where Δ is        a number that renders the composition charge neutral,    -   where an average ionic radius ratio of ions in A, A′ and A″-site        holding 8-fold coordination with oxygen to ions in B, B′ and        B″-site holding 6-fold coordination with oxygen is between 1.46        and 1.80.

The distribution of catalytically active metals throughout the structureof a pyrochlore creates an active and well dispersed metal bound in thecrystal structure, reducing the metal sintering that typically occurs onsupported catalysts used in reforming reactions. It is believed thatsmaller metallic sites are less susceptible to poisoning by sulfur orcarbon than larger ones, thus, distributing the metal throughout thestructure may decrease catalyst deactivation by sulfur and carbon.Further, oxygen mobility may also be enhanced by the exchange of variouselements at A and B sites in the pyrochlore.

Exemplary pyrochlore material catalyst preparation and use in reformingare demonstrated herein. The pyrochlore material catalysts exhibitstable performance under the reaction conditions utilized for catalyticpartial oxidation (CPOX), steam reforming (SR), dry reforming (DR), andoxidative steam reforming (OSR).

The various features of novelty which characterize this disclosure arepointed out with particularity in the claims annexed to and forming apart of this disclosure. For a better understanding of the invention,its operating advantages and specific objects attained by its uses,reference is made to the accompanying drawings and descriptive matter inwhich a preferred embodiment of the disclosure is illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary pyrochlore structure.

FIG. 2 illustrates an exemplary set-up for reforming reactions using thepyrochlore material catalyst.

FIG. 3 illustrates exemplary results for oxidative steam reformingconducted over 1000 hours using an embodiment of the pyrochlore materialcatalyst.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The following description is provided to enable any person skilled inthe art to use the invention and sets forth the best mode contemplatedby the inventors for carrying out the invention. Various modifications,however, will remain readily apparent to those skilled in the art, sincethe principles of the present invention are defined herein specificallyto provide a method of catalytically reforming a reactant gas mixtureusing a pyrochlore catalyst material with catalytically active metalssubstituted within the structure of the pyrochlore, to produce a gaseousmixture comprised of at least hydrogen and carbon monoxide using athermally stable catalyst having resistance to both sulfur poisoning andcarbon deposition.

As used herein, the term “pyrochlore material catalyst” means a catalystmaterial comprised of one or more pyrochlores having the compositionA_(2-w-x)A′_(w)A″_(x)B_(2-y-z)B′_(y)B″_(z)O_(7-Δ), where the pyrochlorematerial catalyst may also be comprised of one or more of an othercrystal phase including simple oxide, perovskite, fluorite, weberite,and others, and wherein the pyrochlore material catalyst may be eitherself-supported or structurally supported on a substrate such asaluminas, silicas, mixed metal oxides, and other substrates known in theart, and combinations thereof.

The improved performance of the pyrochlore material catalyst disclosedherein results from the distribution of catalytically active metalsthroughout the structure of a pyrochlore, creating an active, stable,and well dispersed metal incorporated within the crystal structureitself. This greatly reduces the metal sintering that typically occurson supported catalysts used in reforming reactions, and reducesdeactivation by sulfur and carbon. Generally speaking, and without beingbound by theory, it is believed that smaller metallic sites are lesssusceptible to poisoning by sulfur or carbon than larger ones. Further,oxygen mobility may also be enhanced by elemental exchange of variouselements at the A and B sites in the pyrochlore. Oxygen mobility is alsoan identified mechanism for the reduction of carbon accumulation on thesurface in reforming reactions.

A pyrochlore is composed of ½ trivalent cations and ½ tetravalentcations in a cubic cell structure, with the general stoichiometryA₂B₂O₇. The A-site is usually a large cation (typically rare earthelements) and is coordinated with eight oxygen atoms. The B-site cationhas a smaller radius (usually transition metal) and is coordinated withsix oxygen atoms. In order to form a stable pyrochlore, A and B cationsmust have an ionic radius ratio r_(A)/r_(B) between 1.46 and 1.80. Whenmore than one A and/or B metal cations are present in the pyrochlore,these radii are calculated as the average weighted radii by the relativeamounts of each species present therein. A typical pyrochlore structureis shown at FIG. 1. See also Subramanian et al, “Oxide Pyrochlores—AReview,” Progress in Solid State Chemistry, 15 (1983).

Applicants have found that substituting for A and B cations alters thecatalytic activity and resistance to deactivation in reformingreactions. A wide range of elements can be substituted into thepyrochlore lattice while maintaining the distinctive pyrochlorestructure. With the proper selection, substitution of cations into theA-site results in improved oxygen-ion conductivity and promotes carbonoxidation in the material at elevated temperatures, which limits carbonaccumulation during the reforming reaction. Meanwhile, substitution ofthe B-site cations with an active reforming metal can be used to improvethe catalytic activity of the material. Metal substituted into theB-site retain high activity and selectivity after substitution into thepyrochlore while elements substituted at the A-site promote and furtherimprove the activity, which significantly reduces carbonaceous depositson the pyrochlore catalyst.

Generally speaking and without being bound by theory, H₂ and CO yieldsfor the pyrochlore material catalysts do not decrease continuously inthe presence of aromatic and organic sulfur compounds, but ratherslightly drop to lower, but stable, levels. This is evidence of kineticinhibition of the active catalytic sites by the contaminants rather thancatalyst deactivation. In addition, olefins—a product of non-catalyticreforming—remain low after aromatic and organic sulfur contaminantspecies are added to the reactant gas mixture, indicating that theB-site dopants in the pyrochlore structure help retain catalyticactivity in the presence of the contaminants. Further, after thecontaminants are removed, olefin yields return to essentially zeroconcentration and the H₂ and CO yields produced recover. Collectively,these results could be explained by a rapid (but limited) deposition ofsurface species derived from or caused by the aromatic and organicsulfur compounds, which limits the approach to equilibrium H₂ and COyields on the pyrochlore while not continuously accumulating on thesurface of the doped pyrochlore.

Thus, provided herein is a method of catalytically reforming a reactantgas mixture, comprising providing a reactant gas mixture comprised ofhydrocarbons and an oxidant, and providing a pyrochlore materialcatalyst comprised of one or more pyrochlores having the compositionA_(2-w-x)A′_(w)A″_(x)B_(2-y-z)B′_(y)B″_(z)O_(7-Δ) where:

-   -   A is a trivalent ion of an element selected from the group        consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Er, Tm,        Yb, Lu, Bi, Sc, Y, In, and Tl,    -   A′ is a trivalent ion of an element not equivalent to A and        selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm,        Eu, Gd, Tb, Dy, Er, Tm, Yb, Lu, Bi, Sc, Y, In, and Tl, and        wherein 0≦w≦1,    -   A″ is a divalent ion selected from the group consisting of Mg,        Ca, Sr, and Ba, and wherein 0≦x<1 and w+x≦1,    -   B is a tetravalent ion of an element selected from the group        consisting of Ti, Cr, Mn, Zr, Mo, Tc, Rh, Pd, Hf, Os, Ir, Pt,        Si, Ge, Sn, and Pb,    -   B′ is a trivalent ion or a tetravalent ion of an element        selected from the group consisting of Mo, Fe, Os, Ru, Co, Rh,        Ir, Ni, Pd, Pt, Cu, Re and V, wherein if B′ is a tetravalent ion        then B′ is an element not equivalent to B, and wherein 0<y≦1,    -   B″ is a divalent ion, a trivalent ion, or a tetravalent ion of        an element selected from the group consisting of Mg, Ca, Sr, Ba,        Y, Ce, Re, Cr, Ti, Zr, Hf, Ni, Co, V, and Mo, wherein if B″ is a        trivalent ion B″ is an element not equivalent to B′, and if B″        is a tetravalent ion than B″ is an element not equivalent to B′        and not equivalent to B, wherein 0≦z<1 and y+z≦1, and where Δ is        a number that renders the composition charge neutral,    -   where the average ionic radius ratio of ions in A, A′ and        A″-site holding 8-fold coordination with oxygen to ions in B, B′        and B″-site holding 6-fold coordination with oxygen is between        1.46 and 1.80. The reactant gas mixture is contacted with the        pyrochlore material catalyst at conditions of temperature,        pressure and gas flow rate during the contacting to promote a        catalytic reforming process and produce a gaseous mixture        comprised of at least hydrogen and carbon monoxide.

Any suitable reaction regime may be applied in order to contact thereactant gas mixture with the pyrochlore material catalyst. One suitableregime is a fixed bed reaction regime, in which the catalyst is retainedwithin a reaction zone in a fixed arrangement. Particles of thepyrochlore catalyst material may be employed in the fixed bed regime,retained using fixed bed reaction techniques well known in the art.Alternatively, the catalyst may be in the form of a pellet, foam,honeycomb, monolith, or other geometry advantageous in facilitatingcontact. The pyrochlore material catalyst may be supported on asubstrate such as aluminas, silicas, and mixed metal oxides, and othersubstrates known in the art.

The reactant gas mixture is contacted with the pyrochlore materialcatalysts in a reaction zone maintained at conversion-promotingconditions effective to produce an effluent stream comprising carbonmonoxide and hydrogen. The reactant gas mixture may be comprised of oneor more of natural gas; methane, liquefied petroleum gas comprised ofC2-C5 hydrocarbons; diesel, jet fuels, gasoline, JP fuels, tars, andkerosene comprised of C6+ heavy hydrocarbons; oxygenated hydrocarbonssuch as biodiesel, alcohols, and dimethyl ether, and methane. Thereactant gas mixture may be comprised of diesel having a sulfur contentgreater than 14 parts per million by weight. The reactant gas mixturemay be comprised of diesel and aromatics, where the aromatic content isgreater than 20 weight percent, with greater than 35 weight percent ofthe aromatic content being multi-ring aromatics. It is understood thatthe foregoing examples constitute exemplary hydrocarbon sources only andare not meant to limit the disclosure herein.

The ratio of oxygen to carbon in the reactant gas mixture may vary, withthe mixture dependent on the particular hydrocarbons chosen and theamount of oxygen necessary to conduct the particular partial oxidationreaction, as is known in the art. Preferably, the reactant gas mixturehas an overall oxygen to carbon atomic ratio equal to or greater than0.9.

The catalytic reforming process may be catalytic partial oxidation usingone or more of air or oxygen as an oxidant. The catalytic reformingprocess may also be steam reforming using steam as an oxidant. Thecatalytic reforming process may also be oxidative steam reformingoxidant using one or more of air, oxygen, or steam as an oxidant. Thecatalytic reforming process may also be CO₂ reforming using carbondioxide as an oxidant or any combination of oxidant thereof.

EXAMPLES Catalyst Preparation

Catalysts may be prepared using the Pechini Method. See U.S. Pat. No.3,330,697, issued to Pechini, issued on Jul. 11, 1967. Sources of themetal cations A, A′, A″, B, B′, or B″ include compounds of those cationsand mixtures thereof. An exemplary preparation method follows:

Metal nitrate precursors and citric acid are dissolved separately intodeionized water. The citric acid/metal molar ratio may be from 1.0-1.5,preferably about 1.2. Aqueous metal salts are then combined into abeaker and stirred. To this mixture, aqueous citric acid is added. Thesolution is then heated to 65° C. under stirring. At 65° C., ethyleneglycol is added. The ethylene glycol/citric acid ratio may be from1.0-4.0, preferably about 1.0. The solution is then stirred continuouslyat temperature until most of the water has evaporated and a viscous,transparent resin remains. The beaker is then transferred into a heatingmantle pre-heated to 65° C. The temperature of the mantle is increasedto 130° C. to promote a polyesterfication reaction between the citricacid and the ethylene glycol. The formed catalyst intermediate is thenplaced into an oven to dry. Following drying, the organic precursor iscalcined at 1000° C. Ramp rate for the calcination step is 5° C./min.

An alternate preparation method is co-precipitation: Metal saltprecursors are dissolved into de-ionized water to form a 1M solution.The metal solution is then added dropwise into a solution containingexcess ammonium carbonate (1M). Next, the formed precipitate is aged for6 hours at 60° C., vacuum filtered to separate precipitate, then rinsedand dried. Precursor is then calcined at 1000° C. for 8 hours using aramp rate for calcination of 5° C./min.

It will be apparent to those skilled in the art that the foregoingpreparation methods are presented by way of example only. Variousalterations, improvements, and modifications to the presentedpreparation methods are within the scope and spirit of the presentdisclosure.

Catalyst Testing:

Catalysts synthesized by the exemplary methods were tested for catalyticpartial oxidation (CPOX), steam reforming (SR), dry reforming (DR), andoxidative steam reforming (OSR) of a surrogate logistic fuel mixture,biodiesel, and commercial Diesel Fuel-2 (DF-2). The catalyst testingtook place in a fixed-bed continuous-flow reactor, shown in FIG. 2. Massflow controllers 201 and 202 were used to deliver N₂ and air/CO₂ to thesystem, while the hydrocarbon fuel and water were fed to the reactor bysyringe pumps 203 and 204. The feed components passed throughpre-heating coils 205 through 208 as illustrated prior to the reactorinlet to ensure complete vaporization of the fuel and thorough heatingof the gases. N₂ was used as a carrier gas to transport the vaporizedhydrocarbon to the reactor tube inlet, where the fuel/N₂ and oxidantcombined before they entered the catalytic reactor 209. A hot box 210heated by convection heater 211 surrounded the catalytic reactor 209 tovaporize the fuel and maintain uniform inlet and product gastemperatures. The hot box temperature was set to 375° C. and controlledby a programmable temperature controller. Fixed bed 212 containing thecatalyst was positioned in the center of an 8 mm i.d. tubular catalyticreactor section and diluted with quartz sand (up to 3 ml) of the sameparticle size as the catalyst to minimize temperature gradients andchanneling throughout the bed. Heat was supplied via a split tubefurnace 213 encapsulating catalytic reactor 209. Bed temperature wasmeasured by an axially centered thermocouple 214 and was controlled by aprogrammable controller. Reactor pressure was maintained by backpressure regulator 215 and pressure gauge 218 provided pressureindications.

Post-reactor, water was condensed out of the gas stream. Compositions ofH₂, CO, CO₂, and CH₄ in the dry gas were analyzed by a mass spectrometer216. Larger hydrocarbon products (C₂-C₆) were measured by a gaschromatograph 217. Carbon balances for all experiments were 100±10%.

The surrogate fuel mixture used in this testing was a combination ofmodel compounds chosen to represent common diesel fuel components.n-Tetradecane (TD), 1-methlynaphthalene (MN), and dibenzothiophene (DBT)were the model compounds used in some of these studies, representingparaffin, aromatic, and sulfur compounds respectively.

Experimental conditions for catalytic partial oxidation (CPOX), steamreforming (SR), dry reforming (DR), and oxidative steam reforming (OSR)were as listed in Table 1.

TABLE 1 Reaction conditions for reforming experiments Reactor ConditionsCPOX SR DR OSR O/C ratio 1.2; 1.3 — 3.0^(a) 1.0 S/C ratio — 3.0  — 0.5Gas Flow (sccm) 400 400 400 400 WHSV (scc/g_(catalyst)/h) 25,000 & 25,000 25,000 25,000 50,000 Pre-heat Temperature (° C.) 375 375 375 375Bed Temperature (° C.) 900 900 900 900 Pressure (MPa) 0.23 0.23 0.230.23 Catalyst Bed (mg) 480; 960 960 960 960 ^(a)carbon in O/C does notinclude carbon from CO₂Catalysis Testing Results—CPOX:

CPOX results from catalysts prepared by the exemplary methods arepresented below in Tables 2 and 3. H₂, CO, CO₂ and CH₄ values in Table 2are instantaneous values taken after 2 hours time on stream during theCPOX of a surrogate diesel fuel mixture and are presented as % dry gasvolume. H₂, CO, CO₂ and CH₄ values in Table 3 are instantaneous valuestaken after their respective listed times on stream (TOS) during theCPOX of a surrogate diesel fuel mixture, diesel fuel-2 or biodiesel andare presented as % dry gas volume. Results are presented with respect tothe pyrochlore comprising the pyrochlore material catalyst. Duringextended runs listed in Table 3, the pyrochlore material catalystsexhibited stable performance under reaction conditions stated under CPOXin Table 1, in terms of H₂ and CO produced, for at least 9 hours onstream and up to 60 hours with minimal sign of deactivation (i.e. 5%loss from initial H₂ and CO product compositions). The amount of olefinsformed is also a measure of activity loss. Their presence indicatesgas-phase (non-catalytic) chemistry occurring in the reactor. Olefinyields remain low for some of the catalysts during the extended runslisted in Table 3, further indicating the potential stability of therespective pyrochlore material catalyst under these conditions.

TABLE 2 Catalyst formulations and corresponding instantaneous productcomposition (dry gas basis) taken after 2 h time on stream (TOS) duringthe CPOX of 5 wt % MN + 50 ppmw DBT/TD at O/C = 1.2. % % % % % CatalystH₂ CO CO₂ CH₄ Olefins La_(1.5)Sr_(0.5)Zr_(1.73)Ni_(0.28)O_(7-Δ) 14.0714.84 4.98 1.97 1.04 La_(1.5)Sr_(0.5)Zr_(1.95)Pt_(0.05)O_(7-Δ) 16.4716.87 3.79 1.58 0.30 La_(1.5)Sr_(0.5)Zr_(1.95)Rh_(0.05)O_(7-Δ) 18.4818.50 2.84 1.21 0.04 La_(1.5)Sr_(0.5)Zr_(1.95)Ru_(0.05)O_(7-Δ) 17.7117.85 3.29 1.26 0.20 La_(1.97)Mg_(0.03)Zr_(1.95)Rh_(0.05)O_(7-Δ) 17.6217.86 2.97 1.40 0.10 La_(1.9)Ca_(0.1)Zr_(1.95)Rh_(0.05)O_(7-Δ) 18.9118.83 2.51 1.08 0.01 La_(1.97)Sr_(0.03)Zr_(1.95)Rh_(0.05)O_(7-Δ) 18.2818.54 2.71 1.26 0.04 La_(1.99)Ba_(0.01)Zr_(1.95)Rh_(0.05)O_(7-Δ) 18.3718.90 2.53 1.33 0.02 La_(1.5)Ce_(0.5)Zr_(1.95)Rh_(0.05)O_(7-Δ) 16.8916.90 3.64 1.63 0.30 La_(1.5)Gd_(0.5)Zr_(1.95)Rh_(0.05)O_(7-Δ) 17.0516.60 3.78 1.43 0.38 La_(1.5)Sm_(0.5)Zr_(1.95)Rh_(0.05)O_(7-Δ) 15.2215.37 4.44 1.72 0.79 La_(1.5)Y_(0.5)Zr_(1.95)Rh_(0.05)O_(7-Δ) 17.2917.90 3.14 1.42 0.13 La_(1.5)Y_(0.5)Zr_(1.95)Ru_(0.05)O_(7-Δ) 18.4818.21 3.41 1.07 0.08La_(1.67)Ce_(0.25)Ca_(0.08)Zr_(1.94)Rh_(0.06)O_(7-Δ) 18.49 18.77 2.471.15 0.01 La_(1.67)Ce_(0.25)Ca_(0.08)Zr_(1.94)Ru_(0.06)O_(7-Δ) 17.4817.80 3.01 1.44 0.16La_(1.67)Gd_(0.25)Ca_(0.08)Zr_(1.94)Rh_(0.06)O_(7-Δ) 18.36 18.48 2.661.16 0.04 La_(1.67)Gd_(0.25)Ca_(0.08)Zr_(1.94)Ru_(0.06)O_(7-Δ) 17.7617.97 2.95 1.39 0.13 La_(1.64)Y_(0.25)Ca_(0.11)Zr_(1.94)Rh_(0.06)O_(7-Δ)18.30 18.45 2.62 1.29 0.04La_(1.64)Y_(0.25)Ca_(0.11)Zr_(1.94)Ru_(0.06)O_(7-Δ) 16.99 17.54 3.321.56 0.23

TABLE 3 Catalyst formulations, O/C ratio, fuel, TOS, and correspondinginstantaneous product composition (dry gas basis) taken after listed TOSduring the CPOX studies. O/C TOS % % % % % Catalyst Ratio Fuel (h) H₂ COCO₂ CH₄ Olefins La_(1.9)Ca_(0.1)Zr_(1.95)Rh_(0.05)O_(7−Δ) 1.2 5 wt % 1317.86 18.20 3.00 1.40 0.29 MN + 50 ppmw DBT/TDLa_(1.5)Y_(0.5)Zr_(1.95)Ru_(0.05)O_(7−Δ) 1.2 5 wt % 30 16.35 15.89 4.541.68 0.59 MN + 50 ppmw DBT/TDLa_(1.64)Y_(0.25)Ca_(0.11)Zr_(1.94)Rh_(0.06)O_(7−Δ) 1.2 5 wt % 58 16.5717.05 3.71 1.55 0.48 MN + 50 ppmw DBT/TDLa_(1.7)Y_(0.25)Mg_(0.05)Zr_(1.94)Rh_(0.06)O_(7−Δ) 1.2 5 wt % 21 16.0516.95 3.80 1.32 0.13 MN + 50 ppmw DBT/TDLa_(1.7)Y_(0.25)Mg_(0.05)Zr_(1.94)Ru_(0.06)O_(7−Δ) 1.2 5 wt % 9 16.0716.87 3.78 1.42 0.25 MN + 50 ppmw DBT/TDLa_(1.69)Y_(0.25)Sr_(0.06)Zr_(1.94)Rh_(0.06)O_(7−Δ) 1.2 5 wt % 48 17.5218.02 3.14 1.46 0.13 MN + 50 ppmw DBT/TDLa_(1.69)Y_(0.25)Sr_(0.06)Zr_(1.94)Ru_(0.06)O_(7−Δ) 1.2 5 wt % 39 15.1815.70 4.38 1.30 0.20 MN + 50 ppmw DBT/TDLa_(1.72)Y_(0.25)Ba_(0.03)Zr_(1.94)Rh_(0.06)O_(7−Δ) 1.2 5 wt % 60 15.9516.57 4.05 1.74 0.77 MN + 50 ppmw DBT/TDLa_(1.89)Ca_(0.11)Zr_(1.64)Rh_(0.11)Y_(0.25)O_(7−Δ) 1.2 5 wt % 44 16.9117.98 3.18 1.95 0.44 MN + 50 ppmw DBT/TDLa_(1.92)Ca_(0.08)Zr_(1.69)Rh_(0.06)Ce_(0.25)O_(7−Δ) 1.2 5 wt % 42 16.2216.75 3.71 2.06 0.42 MN + 50 ppmw DBT/TDLa_(1.92)Ca_(0.08)Zr_(1.64)Rh_(0.11)Ti_(0.25)O_(7−Δ) 1.2 Diesel 44 18.3420.60 2.16 0.28 Not Fuel-2 DetectedLa_(1.92)Ca_(0.08)Zr_(1.64)Rh_(0.11)Ti_(0.25)O_(7−Δ) 1.3 Diesel 40 16.9419.55 2.95 0.13 Not Fuel-2 DetectedLa_(1.89)Ca_(0.11)Zr_(1.69)Rh_(0.06)Y_(0.25)O_(7−Δ) 1.2 Biodiesel 2719.90 22.00 2.70 0.13 Not DetectedCatalysis Testing Results—SR:

The steam reforming of commercial low sulfur diesel fuel-2 was performedusing 20 wt % La_(1.89)Ca_(0.11)Zr_(1.64)Rh_(0.11)Y_(0.25)O_(7-Δ)supported on zirconium doped ceria(La_(1.89)Ca_(0.11)Zr_(1.64)Rh_(0.11)Y_(0.25)O_(7-Δ)/ZDC) are presentedbelow in Table 4. H₂, CO, CO₂ and CH₄ values are averaged over 48 hourstime on stream and are presented as % dry gas volume in Table 4. Resultsare presented with respect to the pyrochlore comprising the pyrochlorematerial catalyst. Conditions for this testing were as presented underSR at Table 1. Results show that the pyrochlore catalyst produced stableyields under steam reforming conditions with substantially completeconversion of the diesel fuel.

TABLE 4 Metal loading, hydrocarbon fuel and product composition (dry gasbasis) for SR studies on pyrochlore material catalyst Catalyst Fuel % H₂% CO % CO₂ % CH₄ % OlefinsLa_(1.89)Ca_(0.11)Zr_(1.64)Rh_(0.11)Y_(0.25)O_(7−Δ)/ZDC Diesel Fuel-250.88 14.00 8.34 0.03 Not DetectedCatalysis Testing Results—OSR:

The oxidative steam reforming of commercial low sulfur diesel fuel-2 wasperformed using 20 wt % LaCaZrRhY/ZDC. The catalyst demonstrated stableperformance continuously for over 1000 hours. Resulting H₂, CO, CO₂ andCH₄ values are presented in Table 5, and instantaneous H₂, CO, CO₂ andCH₄ values over the 1000 hours are shown at FIG. 3, presented as % drygas volume. Conditions for this testing were as presented under OSR atTable 1. Results show that the pyrochlore catalyst produced stableyields under oxidative steam reforming conditions with substantiallycomplete conversion of the diesel fuel.

TABLE 5 Metal loading, hydrocarbon fuel and product composition (dry gasbasis) for OSR studies on pyrochlore material catalyst Catalyst Fuel %H₂ % CO % CO₂ % CH₄ % OlefinsLa_(1.89)Ca_(0.11)Zr_(1.64)Rh_(0.11)Y_(0.25)O_(7−Δ)/ZDC Diesel Fuel-225.2 19.0 4.2 0.1 Not DetectedCatalysis Testing Results—DR:

The dry reforming of commercial low sulfur diesel fuel-2 was performedusing 20 wt % La_(1.89)Ca_(0.11)Zr_(1.64)Rh_(0.11)Y_(0.25)O_(7-Δ)/ZDC,and the results are presented below in Table 6. Conditions for thisexperiment were as presented under DR at Table 1. Results show that thepyrochlore catalyst can produce stable yields under dry reformingconditions with substantially complete conversion of the diesel fuel.

TABLE 6 Catalyst formulation, hydrocarbon fuel and product composition(dry gas basis) for DR studies on pyrochlore material catalyst over 3hours TOS. Catalyst Fuel % H₂ % CO % CO₂ % CH₄ % OlefinsLa_(1.89)Ca_(0.11)Zr_(1.64)Rh_(0.11)Y_(0.25)O_(7−Δ)/ZDC Diesel Fuel-28.16 19.8 5.8 0.1 0.1

Thus, presented here is a method of catalytically reforming a reactantgas mixture using a pyrochlore catalyst material that is stable underreaction conditions. The pyrochlore catalyst material utilizescatalytically active metals substituted within the structure of apyrochlore to produce a thermally stable catalyst that resists bothsulfur poisoning and carbon deposition. The pyrochlore catalyst materialmaintains high product selectivity to H₂ and CO in the presence ofaromatics and sulfur species. The pyrochlore catalyst material minimizescatalytically active metal migration to the surface, minimizingformation of a supported metal catalyst under reaction conditions. Thepyrochlore material catalysts exhibit stable performance under thereaction conditions utilized for catalytic partial oxidation (CPOX),steam reforming (SR), dry reforming (DR), and oxidative steam reforming(OSR).

Having described the basic concept of the invention, it will be apparentto those skilled in the art that the foregoing detailed disclosure isintended to be presented by way of example only, and is not limiting.Various alterations, improvements, and modifications are intended to besuggested and are within the scope and spirit of the present invention.Additionally, the recited order of elements or sequences, or the use ofnumbers, letters, or other designations therefore, is not intended tolimit the claimed processes to any order except as may be specified inthe claims. Accordingly, the invention is limited only by the followingclaims and equivalents thereto.

All publications and patent documents cited in this application areincorporated by reference in their entirety for purposes to the sameextent as it each individual publication or patent document were soindividually denoted.

What is claimed is:
 1. A method of catalytically reforming a reactantgas mixture, comprising: providing a reactant gas mixture comprisinghydrocarbons and an oxidant; providing a pyrochlore material catalystcomprised of one or more pyrochlores having the compositionA_(2-w-x)A′_(w)A″_(x)B_(2-y-z)B′_(y)B″_(z)O_(7-Δ) wherein: A is atrivalent ion of an element selected from the group consisting of La,Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Er, Tm, Yb, Lu, Bi, Sc, Y, In, andTl, A′ is a trivalent ion of an element selected from the groupconsisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Er, Tm, Yb, Lu,Bi, Sc, Y, In, and Tl, wherein A′ is an element different from A, andwherein 0≦w≦1, A″ is a divalent ion selected from the group consistingof Mg, Ca, Sr, and Ba, and wherein 0<x<1, B is a tetravalent ion of anelement selected from the group consisting of Ti, Cr, Mn, Zr, Mo, Tc,Rh, Pd, Hf, Os, Ir, Pt, Si, Ge, Sn, and Pb, B′ is a trivalent ion or atetravalent ion of an element selected from the group consisting of Mo,Fe, Os, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Re and V, wherein B′ is anelement different from B, and wherein 0<y≦1, B″ is a divalent ion, atrivalent ion, or a tetravalent ion of an element selected from thegroup consisting of Mg, Ca, Sr, Ba, Y, Ce, Re, Cr, Ti, Zr, Hf, Ni, Co,V, and Mo, wherein 0≦z<1 and y+z≦1, and where Δ is a number that rendersthe composition charge neutral, where an average ionic radius ratio ofions in A, A′ and A″-site holding 8-fold coordination with oxygen toions in B, B′ and B″-site holding 6-fold coordination with oxygen isbetween 1.46 and 1.80; contacting the reactant gas mixture with thepyrochlore material catalyst; and maintaining the reactant gas mixtureand the pyrochlore material catalyst at conditions of temperature,pressure and gas flow rate during the contacting to promote a catalyticreforming process and produce a gaseous mixture comprised of at leasthydrogen and carbon monoxide.
 2. The method of claim 1 wherein thepyrochlore material catalyst is supported on a support structure.
 3. Themethod of claim 2, wherein the support structure is alumina, silica, ora mixed-metal oxide.
 4. The method of claim 1 wherein the pyrochlorematerial catalyst is comprised of the one or more pyrochlores and one ormore of another crystal phase including simple oxides, perovskites,fluorites, weberites.
 5. The method of claim 1 wherein the pyrochlorematerial catalyst is a powder or a fabricated geometry.
 6. The method ofclaim 5 wherein the fabricated geometry is a pellet, foam, honeycomb, ormonolith.
 7. The method of claim 1 wherein the reactant gas mixturetemperature is equal to or above 150° C.
 8. The method of claim 1wherein the reactant gas mixture is comprised of natural gas.
 9. Themethod of claim 1 wherein the reactant gas mixture is comprised ofliquefied petroleum gas comprised of C2-C5 hydrocarbons.
 10. The methodof claim 1 wherein the reactant gas mixture is comprised of C6+ heavyhydrocarbons.
 11. The method of claim 10 wherein the C6+ heavyhydrocarbons are comprised of diesel, jet fuels, gasoline, JP fuels,tars, and kerosene.
 12. The method of claim 1 wherein the reactant gasmixture is comprised of oxygenated hydrocarbons.
 13. The method of claim12 wherein the oxygenated hydrocarbons are comprised of biodiesel,alcohols, and dimethyl ether.
 14. The method of claim 1 wherein thereactant gas mixture is comprised of methane.
 15. The method of claim 1,wherein the reactant gas mixture is comprised of diesel and the sulfurcontent is >14 parts per million by weight.
 16. The method of claim 1,wherein the reactant gas mixture is comprised of diesel and aromatics,where the aromatic content is greater than 20 weight percent, withgreater than 35 weight percent of the aromatic content being multi-ringaromatics.
 17. The method of claim 1, wherein the reactant gas mixtureis comprised of diesel, aromatics, and sulfur, where the aromaticcontent is greater than 20 weight percent, with greater than 35 weightpercent of the aromatic content being multi-ring aromatics, and thesulfur content is >14 parts per million by weight.
 18. The method ofclaim 1 wherein the reactant gas mixture has an overall oxygen to carbonatomic ratio equal to or greater than 0.9.
 19. The method of claim 1wherein the reactant gas mixture is comprised of an oxidant, and theoxidant is a highly oxidized gas stream comprised of oxidants O₂, CO₂,or H₂O.
 20. The method of claim 1 wherein the catalytic reformingprocess is catalytic partial oxidation and the reactant gas mixture iscomprised of an oxidant, and the oxidant is air or oxygen.
 21. Themethod of claim 1 wherein the catalytic reforming process is steamreforming and the reactant gas mixture is comprised of an oxidant, andthe oxidant is steam.
 22. The method of claim 1 wherein the catalyticreforming process is oxidative steam reforming oxidant and the reactantgas mixture is comprised of an oxidant, and the oxidant is comprised ofair, oxygen, and steam.
 23. The method of claim 1 wherein the catalyticreforming process is CO₂ reforming and the reactant gas mixture iscomprised of an oxidant, and the oxidant is carbon dioxide.